Issue: May 17, 2008
Piñon needle scale causes dying of some needles on a piñon twig
Question:
We have several piñon trees that were planted in early 2007. These piñons are on an irrigation system. This spring several of them have needles that look like they are dead and on the same branch there is also new growth. What is causing the dead needles? Could it be piñon needle scale? Will whatever it is spread to my other piñons? Is there anything I can do to cure these trees?
Georgann W.
Answer:
Photinia shrubs grow in much of New Mexico, but often have iron chlorosis problems. Iron chlorosis is a yellowing and sometimes dying of foliage due to an inability of these plants to extract adequate iron from our high pH soils. This may be part of your problem. If so, you will need to add a form of iron that the plant can extract from the soil. Chelated irons (iron combined with organic compounds that release the iron to the plants) are the best way to provide available iron. There are several forms of iron chelates, but according to Dr. Robert Flynn, NMSU Extension Agronomist, one works much better than the others in our calcareous (soils with high levels of calcium and high alkalinity). The preferred iron chelate is iron-EDDHA (this should be written on the label of the product along with the long chemical name that "EDDHA" abbreviates). This is not a permanent solution to the problem and must be added repeatedly (frequency depends on your specific soil conditions). Your local NMSU Cooperative Extension office can help you arrange to have your soil tested and help you interpret the soil test results.
From your question, it seems that your plants died very quickly. This may be due to irrigation problems. Did you water sufficiently? Newly planted shrubs and trees should be watered several times a week for the first growing season. Once again the frequency depends on soil conditions. Clay soils are harder to irrigate because they absorb water slowly, but they retain the water much longer than sandy soils. An organic mulch of bark or wood chips will help the soil retain moisture as well.
The symptoms you described can also be due to over irrigation. If you irrigate too frequently, you may see fungal diseases damaging the roots of your shrubs. Addition of high levels of compost, peatmoss, and manure can cause the soil around the roots to hold too much water and cause root disease problems. Manure can itself be a problem if applied into the planting hole around the roots. Manures often contain high levels of soluble mineral salts that can damage newly forming roots.
There are other shrubs to consider. While it is possible to grow photinia in much of New Mexico, like most other broadleafed evergreens, they can suffer damage in the winter when they loose water more rapidly than they can replace if from frozen or dry soil. Many people choose junipers as a replacement. However, due to the potential for pollen allergies, it is wise to choose female juniper plants that produce the small berry-like cones rather than pollen. Arbor vitae, cypress, and hybrid cypress plants are also commonly used shrubs in New Mexico. In the right location, photinia, some hollies, India hawthorn, and other broadleaf evergreen shrubs can be grown, but they are more difficult. Better adapted broadleaf evergreen include the native mahonia plants (often called algerita and similar vernacular names). They are related to the Oregon grape holly which also grows well here.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.
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